Normally, in the development of wind turbines, a defined nominal air density of, for example, ρ=1.225 kg/m3 is assumed.
From U.S. Pat. No. 7,023,105 B2, a method for controlling a wind turbine having an electric generator using air density data at the location of the wind turbine is known. In the method, the generator is controlled by a control unit which processes the air-density data, controls the generator and adjusts the performance data of the generator in dependence on the air density. In the known method, the elevation of the site of the wind turbine above sea level is taken into account, whereby the lower air density is taken into account in the power curve. In this way, the power, which is to be generated by the wind turbine and which is assigned to a rotor speed and therewith to a specific tip speed ratio, can be correspondingly adapted; that is, this power can be reduced so that the generator torque does not exceed the torque made available via the generator as a consequence of an excitation power fed by the control unit. Overall, the efficiency determined via the power curve is to be maintained and the maximum amount of energy should be taken from the wind.
From U.S. Pat. No. 7,420,289 B2, a method for calculating a power curve for high altitude sites is known. Therein, starting from a relation between the power coefficient CP and the tip speed ratio λ, a relation between the electric output power P and the wind speed is determined.
From United States patent application publication 2008/0112807 A1, a wind turbine is known in which the output power is reduced when the temperature of the ambient air drops below a predetermined threshold value. The reason for the power reduction is that with temperatures below −20° C., the operation of the wind turbine can require other load calculations.
For the effects of the air density on the yield of the wind turbine, it is to be considered that in pitch-controlled wind turbines, a change in the air conditions can lead to aerodynamic stall-effects with an undesired stall.